(a) Field of the Invention
The present invention relates to coating protective film which is used temporarily to protect automotive coating, for example on the automotive body, during transportation and storage of automobiles.
(b) Description of the Related Art
Recently, there has arisen the problem that the value of finished automobiles as merchandize is impaired during transportation or keeping due to damage to coating on automotive body caused by spattered stones, a cloud of sand, dust, iron powder, dropping of birds, acidic rain, gas, etc., or due to deterioration of appearance, such as change of gloss or discoloration. In particular, export automobiles, which require a long-term transportation or storage, have been sustained such damage. To protect the automotive coating from such damage, oil- or water-wax type coating protective agents consisting mainly of paraffins have been applied on the surface of the coating.
The wax type-coating protective agents however are not enough efficacious against iron powder, dropping of birds, acidic rain, or the like, and also have bad effects due to migration into the coating. Further, such agents become difficult to remove after standing outdoors for more than about three months, and the waste liquor generated during removal thereof using solvents causes public hazard or requires troublesome treatments. As disclosed in Japanese Patent Application Kokai Koho (Laid-open) Nos. 2-300281 and 3-221169, it is proposed as an alternative to protect the automotive coating by attaching pressure sensitive adhesive film on the surface of automotive body.
A fundamental property requisite to protective film for automotive coating is that it deteriorates so little during a long-term outdoor exposure as not to pollute the coating, for example, by adhesive transfer. The pressure sensitive films disclosed in the above two official gazettes, however, are insufficient in weatherability to tolerate a long-term outdoor use because the substrates thereof are transparent polyolefin films which have been used for painted steel plates. Further, when being attached on automotive body and exposed outdoors for a long term, such films tend to deteriorate so that pressure sensitive adhesives cannot be peeled together with the substrate from the surface of the automotive body and the remaining pressure sensitive adhesives pollute the automotive coating. In these official gazettes, acrylic pressure sensitive adhesives and polyisobutylene pressure sensitive adhesives are exemplified as the typical examples of the pressure sensitive adhesives. As to acrylic pressure sensitive adhesives, the adhesion strength thereof changes widely with passage of time and increases on a long-term outdoor use, thereby making peeling difficult. Polyisobutylene pressure sensitive adhesives, whose adhesion strength changes little with passage of time, have good peelability, but are disadvantageous in that when used outdoors for a long time, these adhesives are decreased in cohesive power due to the poor weatherability of adhesiveness and are apt to remain on automotive coating.
Further, some automotive coating has low glass transition temperature and is easily deformed even by a very low pressure depending on temperature. Therefore, in case the pressure sensitive adhesive films disclosed in the above official gazettes or those conventionally used for the surface protection of aluminum, stainless steel or painted steel sheet-piles are used to protect automotive coating, these films easily deteriorate depending on the attaching temperature or the term of use, so that the change of surface roughness changes gloss or the print of the films are left due to the stress applied by bubbles or due to the deformation of the film edges. Further, automotive coating contains various additives for improving coating properties. The additives tend to migrate from the coating into the pressure sensitive adhesive layer and form, between the coating and the film, bubbles which are sensitive to stress and leave prints on the coating. Thus the appearance of the coating is severely deteriorated. The resins and additives in automotive coating vary according to the kind of the automotive coating, and polyisobutylene pressure sensitive adhesives need improvement since the adhesion strength thereof changes widely because of their susceptibility to the change of surface polarity and to bleeding additives.